U.S. patent application number 12/301902 was filed with the patent office on 2010-09-30 for film forming method, film forming apparatus, storage medium and semiconductor device.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Masahiro Horigome, Takaaki Matsuoka.
Application Number | 20100244204 12/301902 |
Document ID | / |
Family ID | 38778361 |
Filed Date | 2010-09-30 |
United States Patent
Application |
20100244204 |
Kind Code |
A1 |
Matsuoka; Takaaki ; et
al. |
September 30, 2010 |
FILM FORMING METHOD, FILM FORMING APPARATUS, STORAGE MEDIUM AND
SEMICONDUCTOR DEVICE
Abstract
Provided is a technology capable of obtaining a
fluorine-containing carbon film having a good leakage property,
coefficient of thermal expansion and mechanical strength. The
fluorine-containing carbon film is formed by using active species
obtained by activating a C.sub.5F.sub.8 gas and a hydrogen gas.
Fluorine in the fluorine-containing carbon film comes off together
with H so that the amount of F decreases, thereby accelerating the
polymerization. As a result, a C-dangling bond in the
fluorine-containing carbon is decreased and a leakage current is
reduced. Further, as the polymerization accelerates, the film gets
stronger, so that the fluorine-containing carbon film having a high
mechanical strength such as a high elasticity or a high hardness
can be obtained.
Inventors: |
Matsuoka; Takaaki; (Tokyo,
JP) ; Horigome; Masahiro; (Yamanashi, JP) |
Correspondence
Address: |
PEARNE & GORDON LLP
1801 EAST 9TH STREET, SUITE 1200
CLEVELAND
OH
44114-3108
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
38778361 |
Appl. No.: |
12/301902 |
Filed: |
May 11, 2007 |
PCT Filed: |
May 11, 2007 |
PCT NO: |
PCT/JP2007/059775 |
371 Date: |
November 21, 2008 |
Current U.S.
Class: |
257/632 ;
118/696; 118/723AN; 118/723R; 257/E21.487; 257/E23.001;
438/778 |
Current CPC
Class: |
C23C 16/45565 20130101;
H01J 37/3244 20130101; H01J 37/32192 20130101; H01L 21/02274
20130101; H01J 37/32449 20130101; H01L 21/3127 20130101; C23C 16/26
20130101; H01L 21/0212 20130101; C23C 16/511 20130101 |
Class at
Publication: |
257/632 ;
438/778; 118/723.R; 118/723.AN; 118/696; 257/E23.001;
257/E21.487 |
International
Class: |
H01L 23/58 20060101
H01L023/58; H01L 21/469 20060101 H01L021/469 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2006 |
JP |
2006-145620 |
Claims
1. A film forming method for forming a fluorine-containing carbon
film by using active species obtained by activating a
C.sub.5F.sub.8 gas and a hydrogen gas.
2. The film forming method of claim 1, wherein the hydrogen gas is
mixed with the C.sub.5F.sub.8 gas such that a flow rate ratio of
the hydrogen gas to the C.sub.5F.sub.8 gas is about 20% to 60%.
3. The film forming method of claim 1, wherein the C.sub.5F.sub.8
gas is a gas selected from an octafluorocyclopentene gas, an
octafluoropentyne gas and an octafluoropentadiene gas.
4. The film forming method of claim 1, wherein the
fluorine-containing carbon film is an insulating film included in a
semiconductor device.
5. A film forming method comprising: mounting a substrate to be
subjected to a film forming process on a mounting unit in a
processing vessel; introducing a plasma generating gas from an
upper portion of the processing vessel; vacuum-exhausting an inside
of the processing vessel from a lower side below the substrate;
introducing a C.sub.5F.sub.8 gas into the processing vessel from
between a position corresponding to a height at which the plasma
generating gas is introduced and a position corresponding to a
height of the substrate; introducing a hydrogen gas into the
processing vessel; and converting the C.sub.5F.sub.8 gas and the
hydrogen gas into a plasma by supplying a microwave into the
processing vessel from a planar antenna member installed at the
upper portion of the processing vessel to face the mounting table
and provided with a number of slits along a circumferential
direction.
6. A film forming apparatus comprising: an airtightly sealed
processing vessel including therein a mounting unit for mounting a
substrate thereon; a unit for supplying a C.sub.5F.sub.8 gas into
the processing vessel; a unit for supplying a hydrogen gas into the
processing vessel; a plasma generating unit for supplying an energy
to the C.sub.5F.sub.8 gas and the hydrogen gas to convert the gases
into a plasma; a unit for vacuum-evacuating an inside of the
processing vessel; and a control unit for outputting a control
instruction to each unit to introduce the C.sub.5F.sub.8 gas and
the hydrogen gas into the processing vessel and to convert the
gases into the plasma.
7. The film forming apparatus of claim 6, wherein the plasma
generating unit includes: a waveguide for guiding a microwave into
the processing vessel; and a planar antenna member connected to the
waveguide, installed to face the mounting unit and provided with a
number of slits along a circumferential direction, wherein the unit
for supplying the C.sub.5F.sub.8 gas into the processing vessel
introduces the C.sub.5F.sub.8 gas into the processing vessel from
between a position corresponding to a height of a unit for
supplying a plasma generating gas, which is to be excited by the
microwave, into the processing vessel and a position corresponding
to a height of the substrate mounted on the mounting unit.
8. The film forming apparatus of claim 6, further comprising: a
flow rate control unit for controlling a flow rate of the
C.sub.5F.sub.8 gas and a flow rate of the hydrogen gas supplied
into the processing vessel, wherein the flow rate control unit is
controlled by the control unit to mix the hydrogen gas with the
C.sub.5F.sub.8 gas such that a flow rate ratio of the hydrogen gas
to the C.sub.5F.sub.8 gas becomes about 20% to 60%.
9. The film forming apparatus of claim 6, wherein the
C.sub.5F.sub.8 gas is a gas selected from an octafluorocyclopentene
gas, an octafluoropentyne gas and an octafluoropentadiene gas.
10. A storage medium for storing therein a computer program
executed on a computer and used in a film forming apparatus,
wherein the computer program is composed of steps for executing a
film forming method as claimed in claim 1.
11. A semiconductor device comprising an insulating film made of a
fluorine-containing carbon film formed by a method as claimed in
claim 1.
Description
TECHNICAL FIELD
[0001] The present invention relates to a technology for forming a
fluorine-containing carbon film by using plasma.
BACKGROUND ART
[0002] To achieve high integration of a semiconductor device, a
multilayer wiring structure has been employed. However, with the
progression of miniaturization and high integration, a delay of an
electric signal passing through a wiring (i.e., wiring delay) has
been a problem which impedes a realization of a high speed
operation of the device. Since the wiring delay is proportional to
the product of a wiring resistance and an inter-wiring capacitance,
it is required to lower a resistance of an electrode wiring
material and a dielectric constant of an interlayer dielectric for
insulating each layer in order to shorten the wiring delay. For
this purpose, it has been considered to use copper (Cu) as the
wiring material because it has a lower resistance than
conventionally used aluminum (Al).
[0003] Further, though a porous film (SiCOH film) containing
silicon, carbon, oxygen and hydrogen and having a dielectric
constant of about 2.7 and a sufficient mechanical strength is
gaining attention as the interlayer dielectric, the inventors of
the present invention have considered using a fluorine-containing
carbon film (fluorocarbon film) which is a compound of carbon (C)
and fluorine (F) and has a dielectric constant lower than that of
the SiCOH film.
[0004] The fluorine-containing carbon film is very useful film
because a dielectric constant as low as, for example, about 2.5 or
below can be obtained depending on a selection of a kind of a
source gas. However, to be used as the interlayer dielectric, it
needs to have a low leakage current, and it also needs to have a
sufficient mechanical strength to endure an impact that might be
applied thereto during a manufacturing process of the semiconductor
device or after a formation thereof.
[0005] Moreover, since a heat treating process or a cooling process
is performed in the manufacturing process of the semiconductor
device, the same level of CTE (Coefficient of Thermal Expansion) as
that of a metal used as the wiring material is required. The reason
for this is that if there is a big difference in the CTE between
the interlayer dielectric and the wiring material, there occurs a
difference in the degree of expansion or contraction of the
interlayer dielectric and the wiring material during the heat
treating process or the cooling process, resulting in a film
peeling-off, a disconnection of wiring, or the like. Further, a
thermal stability is also required. Especially, if the thermal
stability of the fluorine-containing carbon film is low, the amount
of degas of fluorine from the film increases, resulting in a
problem such as a corrosion of wiring, a generation of a crack in
the interlayer dielectric, or the like.
[0006] Though various kinds of gases are known as the source gas of
the fluorine-containing carbon film, a C.sub.5F.sub.8 gas, for
example, especially has a merit in that a decomposed product
thereof is likely to create a stereostructure, and a C--F bond is
resultantly enhanced, thus enabling an acquisition of an interlayer
dielectric having a low dielectric constant, a small leakage
current, and a high film strength or a high stress-resistant
property. Patent Document 1 discloses a technology for obtaining a
fluorine-containing carbon film having an original composition or
structure of a source material while suppressing an excessive
decomposition of the source material by lowering an electron
temperature of plasma in a plasma film forming apparatus for
converting the C.sub.5F.sub.8 gas into the plasma.
[0007] However, to realize the practical use of the
fluorine-containing carbon film using the C.sub.5F.sub.8 gas as the
source gas, its current leakage needs to be further reduced, and a
mechanical strength such as a hardness or an elastic rate needs to
be enhanced. Further, desirably, its CTE needs to be reduced closer
to the CTE of the wiring material.
[0008] Here, disclosed in Patent Document 2 is a technology in
which a C.sub.4F.sub.8 gas is used as a source gas of a
fluorine-containing carbon film, wherein by adding a hydrogen gas
to the C.sub.4F.sub.8 gas, a deposition speed of the
fluorine-containing carbon film is ensured, a reduction of film
thickness due to a heat treatment is lowered, and the obtained
fluorine-containing carbon film is given a high adhesivity.
However, this document does not mention anything about obtaining a
sufficient mechanical strength or a high CTE compatibility with the
wiring material by means of adding the hydrogen gas to the
C.sub.4F.sub.8 gas. Thus, the problems intended to be solved by the
present invention is deemed to be difficult to resolve by the
technology of Patent Document 2.
[0009] Patent Document 1: Japanese Patent Application No.
2003-083292
[0010] Patent Document 2: Japanese Patent Laid-open Publication No.
2004-311625 (Paragraphs [0074], [0077] and [0078])
DISCLOSURE OF THE INVENTION
[0011] In view of the foregoing, the present invention provides a
technology capable of obtaining a fluorine-containing carbon film
having desirable leakage property, coefficient of thermal expansion
and mechanical strength.
[0012] For this reason, a film forming method in accordance with
the present invention is for forming a fluorine-containing carbon
film by using active species obtained by activating a
C.sub.5F.sub.8 gas and a hydrogen gas. It is desirable that the
hydrogen gas is mixed with the C.sub.5F.sub.8 gas such that a flow
rate ratio of the hydrogen gas to the C.sub.5F.sub.8 gas is about
20% to 60%. Here, a gas selected from an octafluorocyclopentene
gas, an octafluoropentyne gas and an octafluoropentadiene gas is
used as the C.sub.5F.sub.8 gas. Further, the fluorine-containing
carbon film is used as, for example, an insulating film included in
a semiconductor device.
[0013] Further, a film forming method in accordance with the
present invention includes: mounting a substrate to be subjected to
a film forming process on a mounting unit in a processing vessel;
introducing a plasma generating gas from an upper portion of the
processing vessel; vacuum-exhausting an inside of the processing
vessel from a lower side below the substrate; introducing a
C.sub.5F.sub.8 gas into the processing vessel from between a
position corresponding to a height at which the plasma generating
gas is introduced and a position corresponding to a height of the
substrate; introducing a hydrogen gas into the processing vessel;
and converting the C.sub.5F.sub.8 gas and the hydrogen gas into a
plasma by supplying a microwave into the processing vessel from a
planar antenna member installed at the upper portion of the
processing vessel to face the mounting table and provided with a
number of slits along a circumferential direction.
[0014] Furthermore, a film forming apparatus in accordance with the
present invention includes: an airtightly sealed processing vessel
including therein a mounting unit for mounting a substrate thereon;
a unit for supplying a C.sub.5F.sub.8 gas into the processing
vessel; a unit for supplying a hydrogen gas into the processing
vessel; a plasma generating unit for supplying an energy to the
C.sub.5F.sub.8 gas and the hydrogen gas to convert the gases into a
plasma; a unit for vacuum-evacuating an inside of the processing
vessel; and a control unit for outputting a control instruction to
each unit to introduce the C.sub.5F.sub.8 gas and the hydrogen gas
into the processing vessel and to convert the gases into the
plasma.
[0015] Here, it is desirable that the plasma generating unit
includes: a waveguide for guiding a microwave into the processing
vessel; and a planar antenna member connected to the waveguide,
installed to face the mounting unit and provided with a number of
slits along a circumferential direction, wherein the unit for
supplying the C.sub.5F.sub.8 gas into the processing vessel
introduces the C.sub.5F.sub.8 gas into the processing vessel from
between a position corresponding to a height of a unit for
supplying a plasma generating gas, which is to be excited by the
microwave, into the processing vessel and a position corresponding
to a height of the substrate mounted on the mounting unit.
[0016] Further, it is desirable that the film forming apparatus
further includes: a flow rate control unit for controlling a flow
rate of the C.sub.5F.sub.8 gas and a flow rate of the hydrogen gas
supplied into the processing vessel, wherein the flow rate control
unit is controlled by the control unit to mix the hydrogen gas with
the C.sub.5F.sub.8 gas such that a flow rate ratio of the hydrogen
gas to the C.sub.5F.sub.8 gas becomes about 20% to 60%. A gas
selected from an octafluorocyclopentene gas, an octafluoropentyne
gas and an octafluoropentadiene gas is used as the C.sub.5F.sub.8
gas.
[0017] Furthermore, a storage medium in accordance with the present
invention is for storing therein a computer program executed on a
computer and used in a film forming apparatus, wherein the computer
program is composed of steps for executing the film forming method
as described above. Further, a semiconductor device in accordance
with the present invention includes an insulating film made of a
fluorine-containing carbon film formed by one method among the
above-described methods.
[0018] In accordance with the present invention, since the
fluorine-containing carbon film is formed by using an active
species obtained by activating the C.sub.5F.sub.8 gas and the
hydrogen gas, the fluorine-containing carbon film having a small
leakage current and a high mechanical strength such as a high
hardness or a high elasticity can be obtained, as can be seen from
the later described experimental examples.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is an explanatory diagram for describing a formation
of a fluorine-containing carbon film in accordance with an
embodiment of the present invention;
[0020] FIGS. 2A to 2C are explanatory diagrams for describing a
C.sub.5F.sub.8 gas used in the embodiment of the present
invention;
[0021] FIG. 3 is a cross sectional view of a semiconductor device
in accordance with the embodiment of the present invention;
[0022] FIG. 4 presents an explanatory diagram for describing a
dissociation of the C.sub.5F.sub.8 gas used in the embodiment of
the present invention;
[0023] FIG. 5 is a longitudinal side view illustrating an example
plasma film forming apparatus for use in the embodiment of the
present invention;
[0024] FIG. 6 depicts a plan view of a second gas supplying unit
used in the plasma film forming apparatus;
[0025] FIG. 7 is a perspective view illustrating a partial cross
section of an antenna unit used in the plasma film forming
apparatus;
[0026] FIGS. 8A to 8C are characteristic diagrams showing an XPS
analysis result of a fluorine-containing carbon film;
[0027] FIG. 9 is a characteristic diagram showing a hydrogen gas
flow rate dependency of a leakage current of a fluorine-containing
carbon film;
[0028] FIG. 10 is a characteristic diagram showing an electric
field dependency of a leakage current of a fluorine-containing
carbon film;
[0029] FIG. 11 provides a characteristic diagram showing an
electric field dependency of a leakage current of a
fluorine-containing carbon film;
[0030] FIG. 12 is a characteristic diagram showing a hydrogen gas
flow rate dependency of a hardness of a fluorine-containing carbon
film;
[0031] FIG. 13 is a characteristic diagram showing a hydrogen gas
flow rate dependency of an elasticity of a fluorine-containing
carbon film;
[0032] FIG. 14 sets forth a characteristic diagram showing a
hydrogen gas flow rate dependency of a film forming speed of a
fluorine-containing carbon film;
[0033] FIGS. 15A and 15B present characteristic diagrams showing a
TDS analysis result of a fluorine-containing carbon film;
[0034] FIG. 16 is a characteristic diagram showing a variation of a
film thickness of a fluorine-containing carbon film before and
after a heat treatment;
[0035] FIG. 17 is a characteristic diagram showing a hydrogen gas
flow rate dependency of a dielectric constant of a
fluorine-containing carbon film;
[0036] FIG. 18 offers a characteristic diagram showing a plasma gas
flow rate dependency of a dielectric constant of a
fluorine-containing carbon film;
[0037] FIG. 19 is a characteristic diagram showing a leakage
current and a dielectric constant of a fluorine-containing carbon
film; and
[0038] FIGS. 20A to 20C are explanatory diagrams showing a bonding
energy of each bond of a C.sub.5F.sub.8 gas and a C.sub.4F.sub.8
gas.
BEST MODE FOR CARRYING OUT THE INVENTION
[0039] Hereinafter, an embodiment of a semiconductor device
manufacturing method employing a film forming method in accordance
with the present invention will be described. In the present
embodiment, although a process of forming an insulating film made
up of a fluorine-containing carbon film (CF film) is included, an
embodiment of a method for forming an interlayer dielectric as the
insulating film will be explained. FIG. 1 is a diagram for
illustrating images of the manufacturing method in accordance with
the present embodiment, and employed as a substrate 1 is one having
a transistor circuit and a gate electrode formed on a surface
thereof or one having thereon an n.sup.th layer of a multilayer
wiring structure.
[0040] Further, a C.sub.5F.sub.8 gas, which is a compound of carbon
and fluorine, is used as a source gas 21 for forming the
fluorine-containing carbon film on the substrate 1. In the present
invention, a mixture gas 22 containing a hydrogen gas is used
besides the source gas 21. Here, as for the mixture ratio of the
hydrogen gas, it is desirable that a flow rate thereof relative to
a flow rate of the C.sub.5F.sub.8 gas is about 20% to 80%, as can
be seen from experimental examples to be described later.
[0041] For example, as illustrated in FIGS. 2A to 2C, the
C.sub.5F.sub.8 gas can be a cyclic C.sub.5F.sub.8 gas
(1,2,3,3,4,4,5,5-Octafluoro-1-cyclopentene, see FIG. 2A), a
straight-chain C.sub.5F.sub.8 gas having one triple bond
(1,1,1,2,2,5,5,5-Octafluoro-1-pentyne, see FIG. 2B), a
straight-chain C.sub.5F.sub.8 gas having conjugated double bonds
(1,1,2,3,4,5,5,5-Octafluoro-1,3-pentadiene, see FIG. 2C), or the
like.
[0042] FIG. 3 shows an example semiconductor device including the
interlayer dielectric formed by the present method. Reference
numeral 31 represents a p-type silicon layer, reference numerals 32
and 33 represent n-type regions serving as a source and a drain,
respectively, reference numeral 34 represents a gate oxide film and
reference numeral 35 represents a gate electrode, and these
components constitute a MOS transistor. Further, reference numerals
36 and 37 denote a BPSG film and a wiring made of, e.g., tungsten,
respectively, and reference numeral 38 represents a side spacer. On
the BPSG film 36, interlayer dielectrics 42 are laminated in
multiple layers (FIG. 3 shows only two layers for the simplicity of
explanation), wherein each interlayer dielectric is made up of a
fluorine-containing carbon film of the present invention and has a
wiring layer 41 made of, e.g., copper. Further, reference numeral
43 is a hard mask made of, e.g., silicon nitride; reference numeral
44 denotes a protective layer made of, e.g., titan nitride,
tantalum nitride, or the like for preventing a diffusion of a
wiring metal; and reference numeral 45 denotes a protective
film.
[0043] The present invention is directed to form a
fluorine-containing carbon film by converting the C.sub.5F.sub.8
gas and the hydrogen gas into plasma. If the C.sub.5F.sub.8 gas and
the hydrogen gas are converted into the plasma, decomposed products
containing carbon and fluorine of the C.sub.5F.sub.8 gas, which are
contained in the plasma, are deposited on a surface of the
substrate 1, so that the fluorine-containing carbon film 23 is
formed, and active species of hydrogen act on the decomposed
products or the fluorine-containing carbon film 23.
[0044] As can be seen from the experimental examples to be
described later, though the dielectric constant of the
fluorine-containing carbon film 23 formed by the above-described
method increases slightly higher than that in case without adding
the hydrogen gas to the C.sub.5F.sub.8 gas, it is still possible to
obtain a dielectric constant of about 2.3 to 2.5 by adjusting the
mixing amount of the hydrogen gas and to reduce a leakage
current.
[0045] Moreover, it is also possible to obtain an elasticity of
about 6 to 8 GPa and a hardness of about 0.6 to 0.8 GPa and an
elasticity or hardness 1.5 times as great as that of a plastic
material along with a good mechanical property. Therefore, a
breakdown of the interlayer dielectric can be suppressed in the
manufacturing process of the semiconductor device, e.g., in a CMP
process even in case that a great force is applied thereto, and an
impact that might be applied after the formation of the
semiconductor device can be endured.
[0046] Moreover, since a coefficient of thermal expansion close to
that of copper can be obtained, it is possible to suppress a film
peeling-off or a disconnection between the wiring layer and the
interlayer dielectric by using the copper which is useful as a
wiring material and by using the fluorine-containing carbon film 23
as the interlayer dielectric between each wiring layer.
[0047] Furthermore, when a heat treatment is performed, a corrosion
of wiring or a crack of the interlayer dielectric hardly occurs
because a degassing of the fluorine or carbon is difficult to be
generated. Furthermore, since a degassing amount is very small, a
film thickness hardly changes before and after the heat treatment,
and a thermal stability is good. Furthermore, since a film forming
speed increases as a result of adding the hydrogen gas, it is also
possible to obtain an effect of improving the efficiency of film
formation by using a smaller amount of source gases.
[0048] As mentioned above, though the fluorine-containing carbon
film 23 formed by converting the C.sub.5F.sub.8 gas and the
hydrogen gas into the plasma has the slightly increased dielectric
constant, the leakage current decreases while allowing for the
enhancement of the mechanical strength such as the elasticity or
the hardness, and its CTE compatibility with the copper, which is
useful as the wiring layer, improves. Furthermore, since a basic
film property such as the thermal stability or the film forming
speed also improves, the fluorine-containing carbon film 23 of the
present invention has a good characteristic as the insulating film.
Especially, it is effective to form the wiring layers with the
copper and to use the fluorine-containing carbon film of the
present invention as the interlayer dielectric for insulating the
wiring layers.
[0049] The inventors of the present invention have investigated the
reason why the fluorine-containing carbon film 23 formed by
converting the C.sub.5F.sub.8 gas and the hydrogen gas into the
plasma has superior characteristics as the insulating film and
figured it out as follows. As will be explained later, since the
bonding energy of each bond in the C.sub.5F.sub.8 gas is great, an
excessive dissociation is suppressed even when it is converted into
the plasma. Further, as illustrated in FIG. 4 which exemplifies the
straight-chain C.sub.5F.sub.8 gas having the triple bond, it is
conjectured that the C.sub.5F.sub.8 gas is dissociated into
C.sub.4F.sub.4 after it becomes --CF.sub.3 and --C.sub.4F.sub.5 as
a result of a cleavage of a C--C bond {circle around (1)} or
dissociated into --C.sub.2F.sub.5 and --C.sub.3F.sub.3 as a result
of a cleavage of a C--C bond {circle around (2)}. As described,
since the decomposed products have a great number of C and a large
molecular weight, the amount of C is more abundant when comparing
the amount of C and F in the fluorine-containing carbon film.
Generally, as is well known, it is easy to carry out a
polymerization if an F/C ratio is no greater than 2.
[0050] Meanwhile, if the fluorine-containing carbon film is formed
by mixing the hydrogen gas with the C.sub.5F.sub.8 gas and
converting them into the plasma, F in the film escapes as it
becomes HF, so that the polymerization becomes easier because the
F/C ratio of the fluorine-containing carbon film is further
lowered. However, as can be seen from the experimental examples to
be described later, several tens of atomic % of H remains in the
fluorine-containing carbon film 23. As a result, though the C, F
and H exist together in the film, the thermal stability of the film
is good, so that it is conjectured that the H becomes hydrocarbon
and is kept in a stable state.
[0051] As described above, if the C.sub.5F.sub.8 gas and the
hydrogen gas are used by being mixed with each other, vulnerable F
in the fluorine-containing carbon film escapes, accelerating the
polymerization and thus increasing multiple bonds. Further, since
the H exists in the stable state, it is conjectured that a
C-dangling bond present in the film is bonded with a C- or
H-dangling bond and is terminated so that the C-dangling bond
present in the film decreases.
[0052] This hypothesis also complies with the following facts: the
dielectric constant slightly increases because of the increase of
C--C bonds in the film; the leakage current is reduced as a result
of the reduction of the C-dangling bond in the film due to the
suppression of a generation of a leakage current caused by the
presence of the dangling bond; the mechanical strength of the film
is enhanced due to the increase of multiple bonds between the C
atoms causing the film to be stronger; and the thermal stability
improves due to the reduction of the escape of the F atoms during
the heat treatment process because the amount of F in the film
decreases.
[0053] Now, a plasma film forming apparatus for forming the
fluorine-containing carbon film 23 by converting the C.sub.5F.sub.8
gas and the hydrogen gas into the plasma will be simply explained
with reference to FIGS. 5 to 7. This plasma film forming apparatus
is a CVD (Chemical Vapor Deposition) apparatus for generating the
plasma by using a radial line slot antenna. In the figures,
reference numeral 5 denotes a processing vessel (vacuum chamber)
having, for example, a cylindrical shape as a whole, and a sidewall
and a bottom portion of the processing vessel 5 are made up of a
conductor, e.g., aluminum containing stainless steel or the like,
and a protective film made of aluminum oxide is formed on an inner
wall surface.
[0054] A mounting table 51 serving as a mounting unit for mounting
thereon a substrate, e.g., a wafer W, is installed in approximately
a center of the processing vessel 5 by interposing an insulator
51a. The mounting table 51 is formed of, for example, aluminum
nitride (AlN) or aluminum oxide (Al.sub.2O.sub.3), and incorporates
therein a cooling jacket 51b through which a coolant is circulated;
and a non-illustrated heater which constitutes a temperature
control unit is installed along with the cooling jacket 51b. A
mounting surface of the mounting table 51 is formed as an
electrostatic chuck. Further, in the mounting table 51, a high
frequency bias power supply 52 of, e.g., about 13.56 MHz is
connected with a non-illustrated electrode, and by allowing the
surface of the mounting table 51 to have a negative potential by
using a bias high frequency wave, ions in the plasma can be
injected with a high verticality.
[0055] A ceiling portion of the processing vessel 5 is opened, and
a first gas supply unit 6 of, for example, a substantially circular
plane shape is disposed in this ceiling portion via a seal member
(not shown) such as an O ring so as to face the mounting table 51.
The gas supply unit 6 is formed of, for example, aluminum oxide,
and formed in its surface facing the mounting table 51 is a gas
flow path 62 communicating with ends of gas supply holes 61. The
gas flow path 62 is connected with one end of a first gas supply
line 63. Meanwhile, the other end of the first gas supply line 63
is connected with a supply source 64 of a plasma generating gas
(plasma gas) such as an argon (Ar) gas or a krypton (Kr) gas and a
supply source 65 of a hydrogen gas serving as a mixture gas. These
gases are supplied into the gas flow path 62 through the first gas
supply line 63 and are uniformly supplied into a space below the
first gas supply unit 6 through the gas supply holes 61.
[0056] In this example, the supply source 64, the first gas supply
line 63 and the first gas supply unit 6 constitute a means for
supplying the plasma generating gas into the processing vessel 5,
while the supply source 65, the first gas supply line 63 and the
first gas supply unit 6 constitute a means for supplying the
hydrogen gas into the processing vessel 5.
[0057] Further, the processing vessel 5 includes a second gas
supply unit 7 of, for example, a substantially circular plane
shape, provided between the mounting table 51 and the first gas
supply unit 6 to divide them, for example. The second gas supply
unit 7 is made up of a conductor such as an aluminum alloy
containing, e.g., magnesium, or an aluminum containing stainless
steel, and a number of gas supply holes 71 are provided in a
surface facing the mounting table 51. Provided inside the gas
supply unit 7 are, as shown in FIG. 6, grid-patterned gas flow
paths 72 communicating with ends of the gas supply holes 71, and
the gas flow paths 72 are connected to one end of a second gas
supply line 73. Further, the second gas supply unit 7 is provided
with a plurality of openings 74 which pass through the second gas
supply unit 7. The openings 74 allow the plasma or a source gas in
the plasma to pass therethrough to reach the space below the gas
supply unit 7, and are provided between the adjacent gas flow paths
72, for example.
[0058] Here, the second gas supply unit 7 is connected with a
supply source 75 of a C.sub.5F.sub.8 gas, which is the source gas,
via the second gas supply line 73, and the C.sub.5F.sub.8 gas is
sequentially flown into the gas flow paths 72 through the second
gas supply line 73 and uniformly supplied into the space below the
second gas supply unit 7 through the gas supply holes 71. In this
example, the supply source 75, the second gas supply line 73 and
the second gas supply unit 7 constitute a means for supplying the
C.sub.5F.sub.8 gas into the processing vessel 5. In the figures, V1
to V3 are valves; reference numerals 101 to 103 are flow rate
control means for controlling supply amounts of the Ar gas, the
hydrogen gas and the C.sub.5F.sub.8 gas into the processing vessel
5, respectively.
[0059] A cover plate 53 formed of a dielectric material such as
aluminum oxide is disposed above the first gas supply unit 6 via a
seal member (not shown) such as an O ring, and an antenna unit 8 is
provided on a top of the cover plate 53 to be in a close contact
therewith. As shown in FIG. 7, the antenna unit 8 includes a flat
antenna body 81 of a circular plane shape having an opening in a
bottom surface thereof; and a circular plate shaped planar antenna
member (slot plate) 82 disposed to block the opening in the bottom
surface of the antenna body 81 and provided with a number of slots.
The antenna body 81 and the planar antenna member 82 are both made
of a conductor, and they form a flat hollow circular waveguide.
Further, a bottom surface of the planar antenna member 82 is
coupled to the cover plate 53.
[0060] In addition, between the planar antenna member 82 and the
antenna body 81, there is disposed a wave shortening member 83 made
of a low-loss dielectric material such as aluminum oxide or silicon
nitride (Si.sub.3N.sub.4). The wave shortening member 83 serves to
shorten a wavelength of a microwave to thereby shorten a wavelength
in the circular waveguide. In the present embodiment, the antenna
body 81, the planar antenna member 82 and the wave shortening
member 83 together form a radial line slot antenna (RLSA).
[0061] The antenna unit 8 configured as described above is mounted
on the processing vessel 5 via a seal member (not shown) such that
the planar antenna member 82 makes a close contact with the cover
plate 53. The antenna unit 8 is connected to an external microwave
generating unit 85 via a coaxial waveguide 84, and supplies a
microwave having a frequency of, for example, about 2.45 GHz or
about 8.3 GHz. An outer waveguide 84A of the coaxial waveguide 84
is connected to the antenna body 81, and a central conductor 84B
thereof is connected to the planar antenna member 82 through an
opening provided in the wave shortening member 83.
[0062] The planar antenna member 82 is made of, e.g., a copper
plate having a thickness of about 1 mm, and is provided with a
plurality of slots 86 for generating, e.g., a circular polarized
wave, as shown in FIG. 7. As for the formation of the slots 86, a
pair of slots 86a and 86b, which are arranged in an approximate
T-shape with a slight interval maintained therebetween, form a
group, and the groups are concentrically or spirally arranged along
a circumferential direction. Since the slots 86a and 86b are
arranged substantially perpendicular to each other, the circular
polarized wave including two perpendicular polarization wave
components is radiated. By arranging each pair of slots 86a and 86b
at an interval corresponding to a wavelength of the microwave
compressed by the wave shortening member 83, the microwave is
radiated as a substantially plane wave from the planar antenna
member 82. In the present invention, the microwave generating unit
85, the coaxial waveguide 84 and the antenna unit 8 together
constitute a plasma generating means.
[0063] Further, a gas exhaust pipe 54 is connected to a bottom
portion of the processing vessel 5, and the gas exhaust pipe 54 is
connected with a vacuum pump 56 serving as a vacuum exhaust means
via a pressure control unit 55 serving as a pressure control means
so that the inside of the processing vessel 5 can be
vacuum-exhausted to a preset pressure level.
[0064] Here, in the above-described plasma film forming apparatus,
the power supply to the microwave generating unit or the high
frequency power supply 52, the opening/closing of the valves V1 to
V3 for supplying the plasma gas or the source gas, the flow rate
control units 101 to 103, the pressure control unit 55, and so
forth are controlled by a non-illustrated control unit based on a
program composed of steps for executing the film formation of the
fluorine-containing carbon film under certain conditions. Further,
at this time, it is also possible to store, in a storage medium
such as a flexible disk, a compact disk, a flash memory or an MO
(Magneto-Optical Disk), a computer program including steps for
executing a control of each component such as the microwave
generating unit 85 and the like, and to control each component
based on this computer program so that the process is performed
under preset conditions.
[0065] Hereinafter, an example of the film forming method in
accordance with the present invention, which is performed by using
the aforementioned apparatus, will be described. First, as a
substrate, a wafer W, on the surface of which a copper wiring is
formed, is loaded into the processing vessel 5 via a
non-illustrated gate valve to be mounted on the mounting table 51.
Subsequently, the inside of the processing vessel 5 is
vacuum-exhausted to a preset pressure level. Further, a plasma gas,
e.g., an Ar gas, to be excited by the microwave is supplied through
the first gas supply line 63 into the first gas supply unit 6 at a
preset flow rate of, for example, about 150 sccm, and a hydrogen
gas as a mixture gas is supplied at a flow rate of about 50 sccm.
Meanwhile, a C.sub.5F.sub.8 gas as a source gas is supplied through
the second gas supply line 73 into the second gas supply unit 7
serving as the source gas supply unit at a predetermined flow rate
of, for example, about 100 sccm. Then, the inside of the processing
vessel 5 is maintained at a process pressure of, for example, about
7.32 Pa (55 mTorr), and a surface temperature of the mounting table
51 is set to be, for instance, about 420.degree. C.
[0066] In the meantime, if a high frequency wave (microwave) of
about 2.45 GHz and 2750 W is supplied from the microwave generating
unit, the microwave propagates through the coaxial waveguide 84 in
a TM mode, a TE mode or a TEM mode to reach the planar antenna
member 82 of the antenna unit 8. Then, the microwave propagates
radially from a central portion of the planar antenna member 82
toward a peripheral portion thereof via the inner conductor 84B of
the coaxial waveguide, during which the microwave is radiated from
the pair of slots 86a and 86b toward the processing space below the
gas supply unit 6 via the cover plate 53 and the first gas supply
unit 6.
[0067] Here, since the cover plate 53 and the first gas supply unit
6 are made of a material, such as aluminum, capable of transmitting
the microwave therethrough, they function as a microwave
transmitting window, so that the microwave is efficiently
transmitted therethrough. At this time, since the pair of slits 86a
and 86b are arranged as described above, a circular polarized wave
is uniformly radiated over the entire plane of the planar antenna
member 82, so that an electric field density in the processing
space thereunder becomes uniform. By the energy of the microwave,
plasma having high density and uniformity is excited over the
entire region of the wide processing space. The plasma is flown
into the processing space below the gas supply unit 7 through the
openings 74 of the second gas supply unit 7, and activates the
C.sub.5F.sub.8 gas supplied into the processing space from the gas
supply unit 7, that is, converts the C.sub.5F.sub.8 gas into the
plasma, thereby generating active species.
[0068] Here, if energy is given to the C.sub.5F.sub.8 gas and the
hydrogen gas, the C.sub.5F.sub.8 gas is decomposed as described
above and resultantly becomes film forming species. The film
forming species transferred onto the wafer W in the aforementioned
way are deposited thereon as a fluorine-containing carbon film.
Though the active species of hydrogen act on the film forming
species or the fluorine-containing carbon film, a CF film formed on
each part of a pattern on the surface of the wafer W is removed by
a sputter etching of Ar ions implanted into the wafer W by a plasma
implantation bias voltage, and the fluorine-containing carbon film
is formed from a bottom portion of a pattern groove while enlarging
its region, so that the fluorine-containing carbon film is buried
in recess portions. The wafer W on which the fluorine-containing
carbon film is formed in this way is unloaded from the processing
vessel 5 via the non-illustrated gate valve. In the foregoing, the
series of operations of loading the wafer W into the processing
vessel 5, performing the process under the preset conditions, and
unloading it from the processing vessel 5 are executed by
controlling each component by means of the control unit or the
program stored in the storage medium.
[0069] If the fluorine-containing carbon film is formed by using
the above-described apparatus, the C.sub.5F.sub.8 gas can be
activated by microwave plasma having a low electron temperature not
higher than about 3 eV. Therefore, an excessive dissociation of the
C.sub.5F.sub.8 gas does not progress, and an excessive
decomposition can be suppressed, so that an original molecular
structure still having the characteristic of the C.sub.5F.sub.8 gas
can be obtained. Accordingly, it is possible to form a
fluorine-containing carbon film having a low dielectric constant, a
low leakage current, a great mechanical strength and a good thermal
stability.
[0070] Moreover, in the above described apparatus, it is also
possible to supply the hydrogen gas into the processing vessel 5
through the second gas supply unit 7, as in the case of supplying
the C.sub.5F.sub.8 gas. Further, the method of the present
invention can also be performed by an apparatus other than the
above-described plasma film forming apparatus as long as the other
apparatus is capable of suppressing the excessive dissociation of
the C.sub.5F.sub.8 gas and activating the C.sub.5F.sub.8 gas such
that the original molecular structure maintaining the
characteristic of the C.sub.5F.sub.8 gas can be obtained.
Experimental Examples
[0071] A. Regarding the composition of the fluorine-containing
carbon film
Experimental Example 1
[0072] By using the plasma film forming apparatus of FIG. 5, a
fluorine-containing carbon film 92 was formed on a silicon bare
wafer 91, which is a substrate, in a thickness of about 150 nm, as
shown in FIG. 8A, and a chemical bonding state of atoms
constituting the fluorine-containing carbon film 92 was examined by
performing an XPS (X-ray Photoelectron Spectroscopy) analysis on a
surface position P1 of the fluorine-containing carbon film 92 and
an inside position P2 of the fluorine-containing carbon film 92.
The measurement at the position P2 was performed by cutting the
fluorine-containing carbon film 92 through the positions P1 to P2,
as shown in FIG. 8A. Here, film forming conditions for the
fluorine-containing carbon film were the same as described above,
and as a C.sub.5F.sub.8 gas, a straight chain C.sub.5F.sub.8 gas
having a triple bond as shown in FIG. 2B was used. The result is
shown in FIG. 8B wherein a solid line and a dashed line indicate
the chemical bonding states of the atoms in the film at the surface
position P1 and at the inside position P2, respectively.
Comparative Example 1
[0073] A fluorine-containing carbon film 92 was formed under the
same conditions as those of the Experimental example 1 except that
the formation of the fluorine-containing carbon film was performed
by using a C.sub.5F.sub.8 gas and an Ar gas at flow rates of about
200 sccm and about 150 sccm, respectively, without using a hydrogen
gas as a mixture gas. Likewise, the XPS analysis was performed with
respect to the surface position P1 and the inside position P2 of
the fluorine-containing carbon film 92. The result is provided in
FIG. 8C wherein though a solid line indicates a chemical bonding
state of atoms in the film at the surface position P1, it is
actually difficult to distinguish data of the surface position P1
and the inside position P2 from each other, and it can be seen that
the chemical bonding states of the atoms in the film at the surface
position P1 and the inside position P2 are substantially
coincident.
[0074] Here, in FIGS. 8B and 8C, a horizontal axis represents a
bond energy and a vertical axis represents an intensity. From these
XPS analysis results, it was acknowledged that though there was
substantially no variation in the composition of the
fluorine-containing carbon film between the surface position P1 and
the inside position P2 in the fluorine-containing carbon film 92 of
Comparative example 1, there occurred a variation in the
composition of the fluorine carbon containing film 92 between the
surface position P1 and the inside position P2 in the
fluorine-containing carbon film 92 of Experimental example 1.
[0075] Further, it was also acknowledged that there hardly occurred
a variation in the composition of the fluorine-containing carbon
film 92 in the surface position P1 depending on whether the
hydrogen gas was added or not, whereas, in the inside position P2,
peaks due to a CF.sub.3 bond, a CF.sub.2 bond and a CF bond are
reduced while peaks due to a C--C bond and a C*--CF.sub.x bond are
increased, as a result of adding the hydrogen gas, so that the
amounts of presence of the CF.sub.3 bond, the CF.sub.2 bond and the
CF bond are reduced, while the amounts of presence of the C--C bond
and the C*--CF.sub.x bond are increased. Moreover, though the
increment of the C--C bond was difficult to detect from FIGS. 8A to
8C, its increase from about 2.5% to about 5.5% was confirmed based
on quantitative data for each component.
Experimental Example 2
[0076] A HFS (Hydrogen Front Scattering) analysis was performed
with respect to the fluorine-containing carbon film 92 of the
Experimental example 1. The analysis result showed that the
fluorine-containing carbon film 92 contains about 53.2 atomic % of
carbon, about 34.5 atomic % of fluorine, and about 12.3 atomic % of
hydrogen.
[0077] From the results of the XPS analysis and the HFS analysis,
it was confirmed that as a result of mixing the hydrogen gas with
the C.sub.5F.sub.8 gas, C, F and H exist in the fluorine-containing
carbon film, and the amount of F decreases while the C--C bond
increases in comparison with the case without adding the hydrogen
gas. This result implies that H is mixed into the
fluorine-containing carbon film during the film forming process and
thus F in the film comes off together with H, so that the amount of
F decreases, resulting in the increase of the C--C bond, a multiple
bond, or a C--H bond.
B. Regarding a Leakage Characteristic
Experimental Example 3
[0078] By using the plasma film forming apparatus of FIG. 5,
fluorine-containing carbon films were formed while varying the
amount of the C.sub.5F.sub.8 gas and the amount of the hydrogen gas
individually, and a leakage current of each fluorine-containing
carbon film was measured, so that a result as shown in FIG. 9 was
obtained. In FIG. 9, a horizontal axis represents (hydrogen gas
flow rate)/(C.sub.5F.sub.8 gas flow rate), and a vertical axis
indicates a leakage current density when an electric field of about
1 MV/cm was applied. In the figure, .largecircle., .DELTA. and
.quadrature. represent data when the C.sub.5F.sub.8 gas flow rate
was about 70 sccm, 85 sccm and 100 sccm, respectively. Further, in
the drawing, indicates data in case that the hydrogen gas was not
mixed (the C.sub.5F.sub.8 gas flow rate was about 200 sccm). In
addition, as the C.sub.5F.sub.8 gas, the straight chain
C.sub.5F.sub.8 gas having a triple bond as shown in FIG. 2B was
employed, and conditions for the film formation were identical with
those of Experimental example 1 except the flow rates of the
C.sub.5F.sub.8 gas and the hydrogen gas.
[0079] As a result, as for the leakage current; it was found that
when using the mixture of the C.sub.5F.sub.8 gas and the hydrogen
gas, the leakage current varies depending on the mixing amount of
the hydrogen gas, and the leakage current tends to increase rapidly
if the mixing amount of the hydrogen gas exceeds a certain level,
though the leakage current decreases in comparison with the case
without mixing the hydrogen gas as long as the flow rate ratio
((hydrogen gas flow rate)/(C.sub.5F.sub.8 gas flow rate)) ranges
from about 0.2 to 0.5. Here, when the flow rate ratio is about 0.8,
the level of the leakage current is almost the same as that of the
case without mixing the hydrogen gas, and when the flow rate ratio
is about 1.0, the leakage current rapidly increases higher than
that of the case without mixing the hydrogen case. Thus, to reduce
the leakage current smaller than that of the case without mixing
the hydrogen gas, it is deemed to be desirable to set the flow rate
ratio to be in a range of about 0.2 to 0.8, i.e., the hydrogen gas
flow rate is set to be no smaller than 20% of the C.sub.5F.sub.8
gas flow rate but no greater than 80% thereof.
Experimental Example 4
[0080] Further, measurement of an electric field dependence of a
leakage current was performed by setting the C.sub.5F.sub.8 gas
flow rate to be about 70 sccm and 100 sccm, and varying the mixing
amount of the hydrogen gas. FIG. 10 shows the result when the
C.sub.5F.sub.8 gas flow rate was 70 sccm, and FIG. 11 shows the
result when the C.sub.5F.sub.8 gas flow rate was 100 sccm. In each
figure, a horizontal axis represents a value corresponding to the
1/2th power of an electric field, while a vertical axis indicates a
value corresponding to (leakage current)/(electric field),
.largecircle., .DELTA., .quadrature. and .diamond. represent data
when the hydrogen gas flow rate was about 20 sccm, 30 sccm, 50 sccm
and 70 sccm, respectively. Further, as the C.sub.5F.sub.8 gas, the
straight chain C.sub.5F.sub.8 gas having a triple bond as shown in
FIG. 2B was employed, and the film formation was performed under
the same conditions as those of Experimental example 1 except the
flow rates of the C.sub.5F.sub.8 gas and the hydrogen gas.
[0081] As a result, it was acknowledged that the value of (leakage
current)/(electric field) gradually decreases as the electric field
increases until the value of the 1/2th power of the electric field
reaches about 600 to 700 (V/cm).sup.1/2 and about 500 to 600
(V/cm).sup.1/2 when the C.sub.5F.sub.8 gas flow rate was 70 sccm
and 100 sccm, respectively, whereas thereafter the value of
(leakage current)/(electric field) gradually increases as the
electric field increases, and the value of (leakage
current)/(electric field) increases as the mixing amount of the
hydrogen gas increases. From this result, it can also be seen that
the leakage current varies depending on the mixing amount of the
hydrogen gas and that the reduction of the leakage current can be
accomplished by optimizing the amount of the hydrogen gas mixed
with the C.sub.5F.sub.8 gas.
C. Regarding Mechanical Strength
Experimental Example 5
[0082] By using the plasma film forming apparatus of FIG. 5,
fluorine-containing carbon films were formed while varying the
amount of the C.sub.5F.sub.8 gas and the amount of the hydrogen gas
individually, and a hardness of each fluorine-containing carbon
film was measured, so that a result as shown in FIG. 12 was
obtained. The measurement of the hardness was performed by a
nano-indentation method. In FIG. 12, a horizontal axis represents a
hydrogen gas flow rate, and a vertical axis indicates a hardness.
In the figure, .largecircle., .DELTA. and .quadrature. represent
data when the C.sub.5F.sub.8 gas flow rate was about 70 sccm, 85
sccm and 100 sccm, respectively. Further, in the figure, indicates
data in case without mixing the hydrogen gas (the C.sub.5F.sub.8
gas flow rate was about 200 sccm). In addition, as the
C.sub.5F.sub.8 gas, the straight chain C.sub.5F.sub.8 gas having a
triple bond as shown in FIG. 2B was employed, and conditions for
the film formation were identical with those of Experimental
example 1 except the flow rates of the C.sub.5F.sub.8 gas and the
hydrogen gas.
[0083] As a result, it was acknowledged that when the hydrogen gas
is added, the hardness of the obtained fluorine-containing carbon
film rapidly increases as the mixing amount of the hydrogen gas
increases, in comparison with the case without mixing the hydrogen
gas in which the hardness was just about 0.35 GPa. Further, it was
also confirmed that when the C.sub.5F.sub.8 gas flow rate was about
70 sccm, the hardness becomes equal to or greater than about 0.6
GPa if the hydrogen gas flow rate becomes about 30 sccm or greater
(i.e., if the flow rate ratio of the hydrogen gas to the
C.sub.5F.sub.8 gas becomes equal to or greater than about 43%); and
when the C.sub.5F.sub.8 gas flow rate was 100 sccm, the hardness
becomes equal to or greater than about 0.6 GPa if the hydrogen gas
flow rate becomes about 55 sccm or greater (i.e., if the flow rate
ratio of the hydrogen gas to the C.sub.5F.sub.8 gas becomes no
smaller than about 55%).
Experimental Example 6
[0084] By using the plasma film forming apparatus of FIG. 5,
fluorine-containing carbon films were formed while varying the
amount of the C.sub.5F.sub.8 gas and the amount of the hydrogen gas
individually, and elasticity of each fluorine-containing carbon
film was measured, so that a result as shown in FIG. 13 was
obtained. The measurement of the elasticity was performed by a
nano-indentation method. In FIG. 13, a horizontal axis represents a
hydrogen gas flow rate, and a vertical axis indicates an
elasticity. In the figure, .largecircle., .DELTA. and .quadrature.
represent data when the C.sub.5F.sub.8 gas flow rate was about 70
sccm, 85 sccm and 100 sccm, respectively. Further, in the figure,
indicates data in case without mixing the hydrogen gas (the
C.sub.5F.sub.8 gas flow rate was about 200 sccm). In addition, as
the C.sub.5F.sub.8 gas, the straight chain C.sub.5F.sub.8 gas
having a triple bond as shown in FIG. 2B was employed, and
conditions for the film formation were identical with those of
Experimental example 1 except the flow rates of the C.sub.5F.sub.8
gas and the hydrogen gas.
[0085] As a result, it was acknowledged that when the hydrogen gas
is added, the elasticity of the obtained fluorine-containing carbon
film rapidly increases as the mixing amount of the hydrogen gas
increases, in comparison with the case without mixing the hydrogen
gas in which the elasticity was just about 4.4 GPa. Further, it was
also confirmed that when the C.sub.5F.sub.8 gas flow rate was about
70 sccm, the elasticity becomes equal to or greater than about 6
GPa if the hydrogen gas flow rate becomes about 20 sccm or greater
(i.e., if the flow rate ratio of the hydrogen gas to the
C.sub.5F.sub.8 gas becomes equal to or greater than about 29%); and
when the C.sub.5F.sub.8 gas flow rate was about 100 sccm, the
elasticity becomes equal to or greater than about 6 GPa if the
hydrogen gas flow rate becomes about 50 sccm or greater (i.e., if
the flow rate ratio of the hydrogen gas to the C.sub.5F.sub.8 gas
becomes no smaller than about 50%).
[0086] As can be confirmed from the above, the hardness and the
elasticity of the fluorine-containing carbon film increase as the
mixing amount of the hydrogen gas with the C.sub.5F.sub.8 gas
increases, so that it is possible to obtain a fluorine-containing
carbon film featuring a hardness of about 0.6 to 0.8 GPa or more
and an elasticity of about 6 to 8 GPa or more.
Experimental Example 7
[0087] In Experimental examples 5 and 6, a coefficient of thermal
expansion was measured for each of the fluorine-containing carbon
film obtained by using the C.sub.5F.sub.8 gas flow rate of about 70
sccm and the hydrogen gas flow rate of about 20 sccm, and the
fluorine-containing carbon film obtained by using the
C.sub.5F.sub.8 gas flow rate of about 100 sccm and the hydrogen gas
flow rate of about 50 sccm. The measurement of the coefficient of
thermal expansion was carried out by an XRR (X-Ray Reflectometry)
method.
[0088] As a result, the coefficient of thermal expansion of the
fluorine-containing carbon film, which was formed with the
C.sub.5F.sub.8 gas flow rate of about 70 sccm and the hydrogen gas
flow rate of about 20 sccm, was about 48 ppm, and the coefficient
of thermal expansion of the fluorine-containing carbon film, which
was formed with the C.sub.5F.sub.8 gas flow rate of about 100 sccm
and the hydrogen gas flow rate of about 50 sccm, was about 39 ppm.
Thus, it was confirmed that the coefficients of thermal expansion
in both cases were smaller than a coefficient of thermal expansion
in case without mixing the hydrogen gas (70 ppm), and approached a
coefficient of thermal expansion of copper (20 ppm).
D. Regarding Film Forming Speed
Experimental Example 8
[0089] By using the plasma film forming apparatus of FIG. 5,
fluorine-containing carbon films were formed while varying the
amounts of the C.sub.5F.sub.8 gas and the hydrogen gas
individually, and a film forming speed of each fluorine-containing
carbon film was measured, so that a result as shown in FIG. 14 was
obtained. In FIG. 14, a horizontal axis represents a hydrogen gas
flow rate, and a vertical axis indicates a film forming speed. In
the figure, .largecircle., .DELTA., .quadrature. indicate data when
the C.sub.5F.sub.8 gas flow rate was about 70 sccm, 85 sccm and 100
sccm, respectively, and indicates data in case without mixing the
hydrogen gas (the C.sub.5F.sub.8 gas flow rate was about 200 sccm).
Further, as the C.sub.5F.sub.8 gas, the straight chain
C.sub.5F.sub.8 gas having a triple bond as shown in FIG. 2B was
used, and conditions for the film formation were identical with
those of Experimental example 1 except the flow rates of the
C.sub.5F.sub.8 gas and the hydrogen gas.
[0090] As a result, it was acknowledged that the film forming speed
increases as the mixing amount of the hydrogen gas increases until
the hydrogen gas flow rate reaches about 50 sccm, though the film
forming speed is smaller than that in the case without mixing the
hydrogen gas if the mixing amount of the hydrogen gas is small.
Accordingly, the result implies that the film forming speed can be
enhanced by optimizing the mixing amount of the hydrogen gas.
E. Regarding Thermal Stability
Experimental Example 9
[0091] By using the plasma film forming apparatus of FIG. 5, a
fluorine-containing carbon film was formed, and a TDS (Thermal
Desorption Spectrometry) analysis was performed with respect to
desorption components H and H.sub.2 from the fluorine-containing
carbon film. The formation of the fluorine-containing carbon film
was performed under the same conditions as described above, and, as
a C.sub.5F.sub.8 gas, the straight chain C.sub.5F.sub.8 gas having
a triple bond as shown in FIG. 2B was used. FIG. 15A shows an
analysis result of the desorption component H, and FIG. 15B shows
an analysis result of the desorption component H.sub.2. Further,
the TDS analysis was also performed for the case without mixing the
hydrogen gas (the C.sub.5F.sub.8 gas flow rate was 200 sccm), and
the result is shown in FIGS. 15A and 15B together. In each of FIGS.
15A and 15B, a horizontal axis represents a wafer temperature, and
a vertical axis indicates a detected intensity of desorption
component.
[0092] As a result, it was confirmed that the detected intensities
of the desorption components H and H.sub.2 are almost constant
regardless of the wafer temperature, and desorption of H and
H.sub.2 does not occur even when the fluorine-containing carbon
film is heated up to 400.degree. C. From this result, it was
confirmed that the fluorine-containing carbon film formed by
converting the C.sub.5F.sub.8 gas and the hydrogen gas into plasma
has a high thermal stability, and H components in the
fluorine-containing carbon film exist in a stable state.
Experimental Example 10
[0093] Further, by using the plasma film forming apparatus of FIG.
5, fluorine-containing carbon films were formed while varying the
hydrogen gas flow rate, and a decrement of a film thickness of each
fluorine-containing carbon film before and after a heat treatment
was measured, and the result is shown in FIG. 16. The conditions
for the film formation of the fluorine-containing carbon film were
identical with those described above except that the C.sub.5F.sub.8
gas flow rate was set to be about 200 sccm, and, as the
C.sub.5F.sub.8 gas, the straight chain C.sub.5F.sub.8 gas having a
triple bond as shown in FIG. 2B was used. Further, the heat
treatment was performed at a temperature of about 400.degree. C.
for about 60 minutes.
[0094] In FIG. 16, a horizontal axis represents a hydrogen gas flow
rate, and a vertical axis indicates a residual thickness ratio. A
residual thickness ratio of 100% implies that there is no
difference in the film thickness before and after the heat
treatment; a residual thickness ratio greater than 100% implies
that the film thickness has increased by the heat treatment; and a
residual thickness ratio smaller than 100% implies that the film
thickness has decreased by the heat treatment. As a result, it was
confirmed that when the hydrogen gas is mixed, the residual
thickness ratio approaches 100%, and a variation in the film
thickness before and after the heat treatment is much smaller than
that in the case without mixing the hydrogen gas. This result
implies that the amount of fluorine or hydrogen (the amount of
degas) desorbed from the fluorine-containing carbon film during the
heat treatment is very small, and thus the thermal stability of the
fluorine-containing carbon film is high.
F. Regarding Dielectric Constant
Experimental Example 11
[0095] By using the plasma film forming apparatus of FIG. 5,
fluorine-containing carbon films were formed while varying the
amounts of the C.sub.5F.sub.8 gas and the hydrogen gas
individually, and a dielectric constant of each fluorine-containing
carbon film was measured, so that a result as shown in FIG. 17 was
obtained. In FIG. 17, a horizontal axis represents (hydrogen gas
flow rate)/(C.sub.5F.sub.8 gas flow rate), and a vertical axis
indicates a dielectric constant. In the figure, .largecircle.,
.DELTA. and .quadrature. indicate data when the C.sub.5F.sub.8 gas
flow rate was about 70 sccm, 85 sccm and 100 sccm, respectively,
and indicates data in case without mixing the hydrogen gas (the
C.sub.5F.sub.8 gas flow rate was 200 sccm). Further, as the
C.sub.5F.sub.8 gas, the straight chain C.sub.5F.sub.8 gas having a
triple bond as shown in FIG. 2B was used, and conditions for the
film formation were identical with those of Experimental example 1
except the flow rates of the C.sub.5F.sub.8 gas and the hydrogen
gas.
[0096] As a result, when the hydrogen gas is not mixed, the
dielectric constant was about 2.2, and it was confirmed that the
dielectric constant increases in proportion to the mixing amount of
the hydrogen gas. Further, from this data, it can be seen that a
flow rate ratio ((hydrogen gas flow rate)/(C.sub.5F.sub.8 gas flow
rate)) desirably needs to be in a range of about 0.2 to 0.6 to
obtain a dielectric constant lower than that of a currently
utilized low-k film, e.g., a SiCOH film; about 0.2 to 0.5 to be
distinguished from the SiCOH film or the like; and about 0.2 to 0.4
to obtain a next-generation low-k film which requires a dielectric
constant of about 2.3 to 2.5.
Experimental Example 12
[0097] Further, a dependency of the dielectric constant upon a
plasma gas flow rate was examined. By using the plasma film forming
apparatus of FIG. 5, fluorine-containing carbon films were formed
with a C.sub.5F.sub.8 gas flow rate of about 70 sccm and a hydrogen
gas flow rate of about 20 sccm, while varying the flow rate of an
Ar gas serving as a plasma gas between about 100 sccm and 250 sccm,
and a dielectric constant of each fluorine-containing carbon film
was measured, and the result is shown in FIG. 18. In the figure, a
horizontal axis represents an Ar gas flow rate, and a vertical axis
indicates a dielectric constant.
[0098] As a result, it was found that the dielectric constant of
the fluorine-containing carbon film decreases with the increase of
the Ar gas flow rate within the Ar gas flow rate ranging from about
100 sccm and 250 sccm. The reason for this is deemed to be as
follows. In the plasma film forming apparatus of FIG. 5, though the
C.sub.5F.sub.8 gas is supplied from the second gas supply unit 7
toward the mounting table 51, dissociated components of the
C.sub.5F.sub.8 gas may be moved to an upper side above the second
gas supply unit 7 while passing through it in the processing vessel
5.
[0099] Here, in the processing vessel 5, an electron temperature in
the upper side above the second gas supply unit 7 is higher than
that in the lower side therebelow. Thus, if the C.sub.5F.sub.8 gas
is introduced into the region above the second gas supply unit 7,
the C.sub.5F.sub.8 gas is divided into pieces because a
dissociation thereof progresses excessively. Therefore, in case
that the amount of the C.sub.5F.sub.8 gas moving toward the upper
side through the second gas supply unit 7 is great, the
C.sub.5F.sub.8 is divided by the excessive dissociation thereof, so
that components having a small number of C and a small molecular
weight increase. As a result, an original molecular structure of
the C.sub.5F.sub.8 gas cannot be maintained, and the characteristic
of the obtained fluorine-containing carbon film is deteriorated,
resulting in an increase of a dielectric constant.
[0100] Meanwhile, if the Ar gas flow rate is increased, since a
great amount of Ar gas is supplied to the upper side above the
second gas supply unit 7, it becomes difficult for the
C.sub.5F.sub.8 gas to move to the upper side above the second gas
supply unit 7. Accordingly, it is believed that the amount of the
C.sub.5F.sub.8 gas moving toward the upper side through the second
gas supply unit 7 would decrease, and the excessive dissociation of
the C.sub.5F.sub.8 gas would be suppressed, so that the original
molecular structure of the C.sub.5F.sub.8 gas can be maintained,
and the deterioration of the characteristic of the obtained
fluorine-containing carbon film would be suppressed, thus enabling
a reduction of the dielectric constant. Thus, it is expected to
obtain a fluorine-containing carbon film having a dielectric
constant of about 2.1 to 2.3 by attempting to optimize the mixing
amount of the hydrogen gas and the amount of the plasma gas with
respect to the C.sub.5F.sub.8 gas.
G. Comparison with the Case of Using a C.sub.4F.sub.8 Gas and a
Hydrogen Gas
Experimental Example 13
[0101] By using the plasma film forming apparatus of FIG. 5,
fluorine-containing carbon films were formed while varying the flow
rates of the C.sub.5F.sub.8 gas and the hydrogen gas, and a
dielectric constant and a leakage current were measured. Further,
as a comparative example, a dielectric constant and a leakage
current were also measured for fluorine-containing carbon films
formed by using only a C.sub.5F.sub.8 gas (without adding the
hydrogen gas) and by using a C.sub.4F.sub.8 gas and a hydrogen gas,
respectively. Further, since the measurement of the leakage current
was performed here under the atmosphere of nitrogen, the
measurement values are much smaller than the aforementioned leakage
current values (e.g., FIG. 9) obtained under the atmospheric
atmosphere.
[0102] FIG. 19 shows the measurement result, wherein X indicates a
case of using the C.sub.5F.sub.8 gas and the hydrogen gas;
.diamond-solid. indicates a case of using only the C.sub.5F.sub.8
gas; and .box-solid. indicates a case of using the C.sub.4F.sub.8
gas and the hydrogen gas. In FIG. 19, a horizontal axis represents
a dielectric constant, and a vertical axis indicates a leakage
current value when an electric field of about 1 MV/cm was applied
to the fluorine-containing carbon film. As a result, it is
confirmed that when the C.sub.5F.sub.8 gas and the hydrogen gas are
used, the leakage current is smaller than that in case of using the
C.sub.4F.sub.8 gas and the hydrogen gas, and the dielectric
constant can be reduced depending on setting of conditions.
[0103] The reason for this is deemed to be as follows. To examine a
bond energy of each bond of the C.sub.5F.sub.8 gas and the
C.sub.4F.sub.8 gas, a cyclic C.sub.5F.sub.8 gas is shown in FIG.
20A; a straight chain C.sub.5F.sub.8 gas is shown in FIG. 20B; and
a C.sub.4F.sub.8 gas is shown in FIG. 20C. A C--C bond energy of
the C.sub.4F.sub.8 gas is found to be lower than any bond energy of
the C.sub.5F.sub.8 gas. Therefore, the dissociation of the
C.sub.4F.sub.8 gas progresses easily in the plasma, and the
C.sub.5F.sub.8 is mainly generated. Accordingly, the resultant
fluorine-containing carbon film basically has a (--CF.sub.2--)n
structure, and this structure remains even if polymerization is
facilitated by adding the hydrogen gas.
[0104] Meanwhile, in case of converting the C.sub.5F.sub.8 gas into
plasma, the excessive dissociation is suppressed as mentioned
above, so that the fluorine-containing carbon film is formed while
maintaining an original molecular structure thereof. For this
reason, it is believed that the fluorine-containing carbon film
formed by using the C.sub.5F.sub.8 gas and the hydrogen gas has
improved film characteristics such as the leakage characteristic,
the dielectric constant, the thermal stability and the like.
H. Summary
[0105] As described above, forming a fluorine-containing carbon
film by combining a C.sub.5F.sub.8 gas and a hydrogen gas is very
effective in consideration of leakage characteristic, hardness,
elasticity, thermal stability and film forming speed. However,
since each value of the leakage characteristic, the hardness, the
elasticity, the thermal stability and the film forming speed can be
varied depending on the amount of the hydrogen gas mixed with the
C.sub.5F.sub.8 gas and the dielectric constant slightly increases
due to the addition of the hydrogen gas, it is required to attempt
to optimize the mixing amount of the hydrogen gas based on these
considerations. The inventors of the present invention have found
that it is desirable to set the mixing amount of the hydrogen gas
such that the flow rate ratio of the hydrogen gas to the
C.sub.5F.sub.8 gas ranges from about 20% to 60% when using the
fluorine-containing carbon film as an insulating film.
* * * * *